The present invention relates generally to gas turbine engines, and, more specifically, to turbine nozzles therein.
In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor for generating hot combustion gases. Energy is extracted from the gases in a high pressure turbine (HPT) which powers the compressor. And, additional energy is extracted from the gases in a low pressure turbine (LPT) which powers a fan in a typical turbofan aircraft engine application.
The HPT includes a first stage turbine nozzle that directly receives the hot combustion gases from the combustor. The nozzle includes a row of hollow stator vanes mounted in inner and outer bands defining corresponding flow passages therebetween for directing the combustion gases into the following row of first stage turbine rotor blades.
In one embodiment, the nozzle includes a mounting flange extending radially inwardly from the inner band which supports the entire nozzle from an annular frame. The mounting flange defines a cavity or plenum on its forward side through which cooling air may be fed into the hollow nozzle vanes. The mounting flange also defines an aft cavity or plenum with the rotary disk of the first stage turbine blades, and through which purge air is channeled during operation.
The hollow nozzle vanes have suitable cooling circuits therein through which a portion of compressor discharge air is channeled for cooling the vanes and bands during operation. The cooling circuits for the first stage turbine nozzle may have various configurations for different engine applications and operating cycles, and are designed for maximizing nozzle life.
Commercial use of one type of aircraft turbofan engine has uncovered elevated operating temperatures in the inner band of the first stage turbine nozzle causing undesirable oxidation thereof in fewer than desired operating cycles. In particular, the aft inner band above the aft purge cavity has shown thermal distress that requires early replacement of the turbine nozzle at corresponding expense and down-time of the aircraft.
Accordingly, it is desired to modify the cooling configuration of this conventional design to improve its durability and life while minimizing the cooling air requirements therefor.